Thanks for your support on this. Good points all.
In the 80’s B party release timeout supervision was two minutes for landline.
I set Vodafone’s original timeout to 45 seconds in 1983. 😉
BT Cellnet (O2) followed suit.
My 5mins was just to make absolutely sure that the “stay on the line” advanced scam would be impossible.
I hope this helps.
I imagine that inbound blocking would work, unless a genuine user tried to call, e.g. a bank!